Sunlight is good for you. Sunlight is also bad for you, but we'll come to that in a bit. For now, let's focus on a five-year study, published this week in the journal Circulation, which shows that vitamin D may offer protection against serious illnesses, including strokes and heart failure, as well as playing a vital role in supporting bone strength. Most people derive the majority of their vitamin D from exposure to the sun - but, it seems, most of us aren't getting enough. While outright deficiency is rare, only around 10% of us have ideal levels of vitamin D.

But peering out at the perpetual gloom of winter, one is forced to wonder: how much sun do we need? And how are we supposed to get it? The good news is that optimising your vitamin D production doesn't necessitate baking in the sun, even when it is out. Short exposures are enough for most people in the UK, with some researchers suggesting that a fair-skinned British adult wearing a T-shirt and trousers needs spend only five to 10 minutes in the midday summer sun to top up their levels of vitamin D. And sun-worshippers will be disappointed to learn that more is not more: once sufficient vitamin D has been produced, the rest is converted into inactive substances. The only thing you'll be doing by lounging around in the UV rays is increasing your chance of developing skin cancer. Happily, vitamin D researchers say you can wear sunscreen and still get your dose of D: one study showed that although sunscreen reduced vitamin D production, it wasn't enough to cause a deficiency.

Of course, there is a dearth of strong sun around just at the moment, but soak it up in more temperate seasons and studies show that vitamin D stored in your fatty tissue will be enough to see you through the winter. If you're concerned about skin cancer - or have darker skin, are pregnant, elderly, wear whole-body coverings, or spend most of your time indoors, all things which carry a greater risk of vitamin D deficiency - you could always take the easy option and throw back a vitamin supplement in the morning.